Electric valve converting system



y 1937- E. F. w. ALEXANDERSON Re. 20,364

- v ELECTRIC VALVE CONVERTING SYSTEM Qriginal Filed March 12, 19 2 Sheets$heet 1 L'- Inventor:

Ernst FWAlexahdersorw j by His Att orne y.

May 18, 1937. E. F. w. ALExANDERsoN Rfl;29,364

ELECTRIC VALVE CONVERTING SYSTEM I Original Filed March 12, 1952 2 Sheets-Sheet 2 Inventor: Ernst F". W. A|e ande1"son,

H is Attorney- Reissued May 18, 1937 UNITED STATES PATENT OFFICE ELECTRIC VALVE CONVERTING SYSTEM Ernst F. W. Alexanderson, Schenectady, N.'Y.,

assignor to General Electric Company, a corporation of New York 47 Claims. 7 (01. 172-274) My invention relates to electric valve converting systems, and more particularly to such systems adapted to transmit energy from an alternating current supply circuit to a variable frequency alternating current load circuit or device, such for example, as an alternating current motor.

Here'tofore, there have been proposed various electric valve converting systems for transmitting 10 energy from an alternating current supply circuit to an electric translating circuit of either constant or variable frequency. In such arrangements it has been customary to interconnect the translating circuit with two groups of grid con- ]5 trolled electric valves which, together with their associated circuits, comprise a pair of rectifiers connected to alternately supply unidirectional current of opposite polarity to the electric translating apparatus. In such arrangements it has been found preferable to use valves of the vapor electric discharge type because of the relatively large amounts of energy which may be handled at ordinary operating voltages. With the use of vapor electric discharge devices in such arrange- ;gs' ments, however, the failure of the grid circuit of any of the electric valves tends to produce a short circuit on the alternating current circuit, or on the electric transmitting apparatus, or both. Furthermore, when utilizing such apparatus for operating an alternating current motor at variable speed, no satisfactory arrangement has been proposed for controlling the electric valves at the various operating speeds of the motor.

It is an object of my invention, therefore, to

pro-vide an improved electric, valve converting system for transmitting energy from an alternating current supply circuit to anelectric translating apparatus which will overcome the above mentioned disadvantages of the arrangements of the prior art, and which will be simple and reliable in operation.

It is a further object of my invention to provide an improved electric valve converting system for transmitting energy from a source of alternating current to an electric translating apparatus in which the occurrence of short circuits on the apparatus or the alternating current supply circuit occasioned by the failure of an electric valve will be substantially eliminated.

It is a further object'of my invention to provide an improved electric valve converting system which is particularly suitable for transmitting energy from an alternating current supply circuit to a variable speed alternating current motor.

It is a still further object of my invention to provide an improved arrangement for controlling the valves of an electric valve converting system which is of general application but which is particularly suitable for controlling the grids of the valves of an electric valve convertin'g system embodying my invention.

In accordance with one embodiment of my invention, an alternating current supply circuit is interconnected with an electric translating apparatus comprising a plurality of phase windings, such for example, as a polyphase alternating current motor, through a plurality of electric valves. One group of electric valves interconnects the supply circuit with one of the phase windings and all of the valves are connected with the same polarity with respect to the alternating current circuit. Similarly, another phase winding of the translating apparatus is connected to the supply circuit through a second group of electric valves, all connected with opposite polarity with respect to the supply circuit, and an interconnection is provided between the two phase windings. With such an arrangement current is continuously fed from the alternating current supply circuit into one phase winding, the valves being so controlled as to periodically transfer it between the several terminals of the winding; is then transmitted through another phase winding; and returned through the valves associated therewith to the alternating current circuit, the return current being periodically transferred between the terminals of the second winding in a similar manner. In this manner the current commutated between the several terminals of a single-phase winding always flows in the same direction so that a failure of the grid circuit of any one of the valves does not cause a short circuit current. In accordance with another feature of my invention when applied to the operation of a variable speed alternating current motor, the interconnection between the several phase windings, which carries unidirectional current, may comprise the field winding of the alternating current motor. When this latter arrangement is used it has been found desirable to control the grids of the several electric valves by means of a distributor driven directly from the motor rotor. For starting the operation of the motor the grid potential for the several valves may be derived from a phase shifting ..circuit energized from the alternating current circuit in order to reduce the average voltage impressed upon the motor armature winding. This alternating potential, variable in phase, is connected in series with the distributor in order to excite the grids of the several electric valves in tromotive force developed by the motor in order the proper sequence. When the motor of such an arrangement reaches a speed of approximately one-half synchronous speed, it has been found preferable to excite the grids of the several electric valves in accordance with the counter-electo operate at the highest efl'lciency.

For a better understanding of my invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings and itsscope will be pointed out in the appended claims. In the drawings, Fig. 1 illustrates an arrangement embodying the several features of my invention for transmitting energy from a single-phase alternating current supply circuit to a quarter phase alternating current motor of the synchronous type, while Figs. 2, 3 and 4 illustrate the power circuits for various polyphase arrangements which are modifications of the circuit of Fig. 1.

Referring now to Fig. 1 of the drawings, there is illustrated an arrangement for transmitting energy from a single-phase alternating current supply-circuit III to a quarter phase alternating current motor ll of the synchronous type comprising armature phase windings l2 and and a rotatable field winding l4. The field winding l4 may be connected in series with'the armature windings, as illustrated, in case it is desired to give the motor series characteristics, or, in case shunt characteristics are desired the field winding may be, separately excited as will bewell understood by those skilled in the art. The terminals of the armature phase winding II are connected to the supply circuit Ill through two pairs of similarly connected electric valves l5l6 and |'|-I3. Similarly, the armature phase winding I3 is connected to supply circuit In through two pairs of electric valves l920 and ill-22 connected oppositely with respect to the valves l5-- l8, inclusive. Each of the several electric valves |522, inclusive, is provided with an. anode, a cathode, and a control grid and may be of any of the several types well known in the art, although I prefer to use valves of the vapor electric discharge'type. The control grids of the pairs of valves I5l5 and l'|l8 are connected, to their respective cathodes through opposite halves of the secondarywindings of thegrid transformers 23 and 24, respectively, current limiting resistor 21 and negative bias batteries 28, although in some instances the batteries 28 may be satisfactorily omitted. Similarly, the grids of the valves of the pairs I9-2ll and 2l22 which have independent cathode potentials are energized through the insulated secondary windings of the transformers 25 and 25, respectively, current limiting resistors 21 and bias batteries 28. In certain instances, it maybe desirable also to connect capacitors 29 directly between the grid and cathode of the several electric valves to eliminate substantially the effect of transients in the power circuit upon the grid control circuit, tending to deprive the grid of its proper control, although this feature comprises no part of my present invention but is disclosed and broadly claimed in 'the copending application of O. W. Livingston,

Serial No. 581,396, filed December 16, 1931, and assigned to the same assignee as the present application. 1

In order'to control the grids of the several electric valves under starting and low speed conditions, there is provided a phase shifting arcurrent circuit l0, and a reactor 32 and variable resistor 33 connected across the transformer 3|, the output circuit being connected between the electrical midpoint of the transformer 3| and the junction between the reactor 32 and resistor 33.- The primary windings of the grid transformers 23-46, inclusive, are energized with the potentials across the resistors 34, 35, 36 and 31, respectively, through a two-position switch 43, while the resistors 343'I, inclusive, are connected in the output circuit of the impedance phase shifting arrangement. 30 through the brushes 38, 39, 4B and 4|, respectively, of a distributor 42 driven directly from the shaft of the motor ll. When the switch '43 is in its right-hand position it will be noted that the several grid transformers 2326, inclusive, are disconnected from the impedance phase shifting circuit 30 and are. short-circuited. However, the feature of controlling the conductivity of the electric valves by a distributor mechanism driven by the motor forms no part of my present invention, but is disclosed and broadly claimed in my United States Letters Patent No. 1,993,581, granted March 5, 1935, assigned to the same assignee as the present application.

It has been found that the above described grid excitation arrangement for the several electric valves operates most satisfactorily for motor speeds less than approximately half synchronous speed, and that most satisfactory operation for higher motor speeds is obtained when the grids of the several electric valves are excited in accordance with the electromotive force. of the motor armature terminals. To secure this type of excitation there is included in the grid circuits of each of the several electric valves l5'22, inclusive, the secondary windings of grid switch 52, when in its right-hand position, is

adapted to short-circuit the transformers 445|, inclusive, and to disconnect them from the rotary phase shifting transformer 54. When. operating with the last described grid excitation, the speed of the motor may be controlled by means of the rotary phase shifting transformer 54, but it has.

beenfound that in some cases a more satisfactory speed control may be obtained by means of a resistor 55 connected in parallel to the field winding I4. With" such an arrangement it' is sometimes desirable to include a reactor 56 in series with parallel circuit comprising the field winding l4 and the resistor 55 in order to compensate for the non-inductive, path through the resistor 55. r

In explaining the operation -of the above described apparatus, it will be assumed that the alternating current circuit I is energized at any desired frequency, preferably a commercial fre quency, that the switch 43 is in its left-hand position, the switch 52 in its'right-hand position,-

conditions, the primary windings of the grid transformers 445I, inclusive, are short-circuited so that no potentials are introduced thereby into the grid circuits of the severalv electric valves and their impedances are negligible. The primary windings of the grid transformers 24 and are energized with the potential appearing a'cross resistors 35 and 36, respectively, through the switch 43, while these resistors are energized with the output potential of the phase shifting circuit through the brushes39 and 4|], respectively, of the distributor 42. For starting the motor II, the resistor 33 is adjusted until the grid potential supplied by the phase shifting circuit 30 is retarded substantially with respect to the potential of the circuit I 0. In this way, electric valves IT and I8 operate together as a rectifier supplying unidirectional current to the upper terminal of the phase winding I2 of the motor II, the current passing from thewinding I2, through the field winding I4, the reactor 56, the left-hand portion of the armature winding I3 and electric valves I 9 and 20, which return the .unidirectional current alternately to the proper sides of the supply circuit III. For example, if the upper side of the circuit I 0 be assumed to be positive initially, current will flow through electric valve I1 and the above traced circuit and will be returned through electric valve 20, since the potential of the lower side of the circuit III is less than that of the upper and since, as is well understood by those skilled in the art, current will flow from a common source through two electric valves connected in parallel to that circuit having the lower counter-electromotive force. By the illustrated connection of the grid transformers, it will be seen that the grids of the valves of each pair IS-IB, III8, etc., re-

ceive potentials. opposite in phase, but since their anode potentials are also opposite in phase, their relative phase displacements are equal. Thus, a relatively low potential unidirectional current is supplied to the upper portion of the phase winding I2 and the left hand portion of the phase winding I3. The distributor 42 is so mounted on the rotorthat in the illustrated position of the distributor the field member I4 is in a maximum torque producing position. When the motor rotor has moved through substantially 90 electrical degrees, assuming a counterclockwise rotation, the energizing circuit of the grid transformer 2-4 through the brush 39 will be broken and the grid transformer 23 will be energized in accordance with the potential across resistor 34, the energizing circuit for which is completed through the brush 38. In a similar manner unidirectional current will now be supplied the lower portion of the phase winding I2 of the motor II thus advancing the axis of resultant magnetization of the motor through 90 electrical degrees so that the motor field member J4 is again in maximum torque producing position. In this manner the current is successively commutated between the terminals of the armature winding I2 and the terminals of the armature winding I3 by means of their associated electric valves, the current always entering through one of the terminals of the phase winding I2, traversing the field winding and being returned from the other phase winding I3 to the circuit III. With this arrangement the current is always commutated between electric valves carrying current in the same direction so that in case the grid circuit of one of the electric valves should fail for any cause, no

short circuit will result on the alternating current supply circuit. At the same time, short circuit currents on the alternating current load circuit, that is the phase windings of the motor II, are prevented, due to the unilateral conductivity characteristics of the electric valves. As the motor II begins to rotate the field winding I4generates a counter-electromotive force in the phase windings I2 and I3 which opposes the fiow of current therethrough so that. the phase of the grid potentials of the several electric valves may be advanced by means of the phase shifting arrangement 30 to increase the average voltage applied to the motor terminals, as is well understood by those skilled in the art.

When the motor II is operating at low speed, the current may be easily commutated between the electric valves associated with the terminals of one of the phase windings, for example, the valves I5 and I1, because of the fact that the electromotive force of the supply circuit periodically passes through zero many times for each cycle of the current supplied to the motor armature winding, and each time that such electromotive force passes through zero the grid of the electric valve may regain control. At higher speeds, however, where the frequency of the supply circuit is of the same order of magnitude as the frequency of the current supplied to the motor armature windings, this type of commutation would become unsatisfactory due to the fact that the successive half cycles supplied to the motor armature windings might comprise different numbers of half cycles-of the supply circuit and thus be unsymmetrical. However, with the above described arrangement, as the motor comes up to speed the field winding I 4 generates a counterelectromotive force in the windings I2 and I3, which is effective to commutate the currentbetween the valves even at an intermediate point in the half cycle of the supply circuit, so that the frequency commutation need not be relied upon. With such an arrangement the motor II may operate at speeds up to and beyond synchronous speed. However, it has been found that the optimum position of the distributor for low speed conditions does not necessarily correspond with that for high speed conditions since the phase of the generated counter-electromotive force may vary with respect to the motor shaft under heavy load conditions.

It has been found that most satisfactory opera- 7 tion at speeds above approximately half synchronous speed may be obtained byexciting the grids .of the several electric valves in accordance with the electromotive force of the motor armature terminals. Such excitation may be obtained by means of the above described apparatus by operating the switch 43 to its right-hand position, thus removing the excitation used for starting the motor and short-circuiting the grid transformers 23-26, inclusive, to minimize their impedance in the grid circuits and operating the switch 52 to its 7 tained by means of a variable resistor connected in parallel with the field winding I4, asillus- 40 one element of which is driven through a pilot trated. With this type of grid excitation and that described in the preceding paragraph, the motor I l, although an alternating current motor or the synchronous type, has speed torque characteristics similar to those of a direct current series motor.

In Fig. 2 there is illustrated a modification of the arrangement shown in Fig. l for transmitting energy from a polyphase alternating current supply circuit to a variable speed polyphase alternating current motor of the squirrel cage induction type. In this figure energy is transmitted from a quarter phase alternating current circuit 'to a quarter phase motor 6! through a plurality of pairs of electric valves 62 connected similarly to the arrangement of Fig. 1 with the exception that energy is drawn from one phase of the alternating current circuit 60, transmitted through the motor SI and returned to the other phase of the alternating current circuit 60. Such an arrangement is somewhat more simple than those described in connection with Figs. 3 and 4 in that only a single pair of electric valves is required for each of the motor terminals, while it has the disadvantage that the current drawn from the polyphase circuit is unbalanced. Such an arrangement is, therefore, particularly suitable for installations comprising a number of relatively small motors energized from the same circuit, so that the unbalance current drawn by one motor may be compensated by that drawn by another. In this arrangement also the synchronous motor ll of Fig. 1 is illustrated as replaced by a-squirrel cage induction motor iii, in which case the field winding is omitted and the electrical neutrals of the phase windings 63 and 64 of the motor 6! are interconnected through a reactance device 65. Also when operating an induction motor, the distributor 42 must be driven at a speed above that of the motor as for example, through a differential gearing 66,

motor 650. This stepping up of the speed of the distributor is necessary in order to determine the slip of the induction motor and thus its speed for any particular load. The connections to the grids are otherwise as in the arrangement illustrated in Fig. 1. When operating a motor of the induction type, however, in'which it inherently draws a lagging current, the current cannot be commutated between theseveral electric valves by the counter-electromotive force 'ot the motor.

so that that feature of grid excitation described in connection with Fig; 1 may be omitted. Otherwise, the operation. is similar to that described in connection with Fig. 1.

In Fig. 3. is illustrated a further modification of the power circuit of Fig. 1 suitable for transmitting energy from a three-phase alternating current supply circuit to a quarter phase motor. The arrangement is similar to Fig. l with the exception that three valves 61 are required for interconnecting each of the motor armature terminals with the three lines of the three-phase alternating current supply circuit 68. The same type of grid control may be utilized as that described in connection with Fig. 1.

or the synchronous type, but, as will be well understood by those skilled in the art, may be of the induction type as illustrated in Fig. 2. The

motor HI comprises two armature windings II and I2 and a field or exciting winding H connected between their neutrals. Each of the several terminals of the armature windings II and I2 is interconnected with each of the lines of the supply circuit 58 through an electric valve 69. The operation and grid control arrangements are similar to that described in connection with Fig. 1.

While I have described my invention as applied to arrangements for transmitting energy from single-phase, quarter phase or three-phase alternating current circuits, to quarter phase or three-phase alternating current motors, it will be obvious to those skilled in the art that my invention is equally'applicable to the transmission of energy between a supply circuit of any number of phases and an alternating current motor of any number of phases.

While I have described what I at present consider preferred embodiments of my-invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope'of my invention.

Whatv I claim as new and desire to secure by- Letters Patent of the United States is:

1. An electric valve converting system comprising a source of alternating current, electric translating apparatus including a plurality of phase windings; a group of similarly connected electric valves iriterconecting one of said phase windings and said source, a second group of electric valves connected oppositely to said first: group windings, an interconnection between saidv phase windings, electric valve means for returning said current from another of said windings to said source, and means for controlling the conductivity of said electric valve means.

3. An electric valve converting system .comprising a source of alternating current, electric translating apparatus including a plurality of phase windings, a group of electric valves connected to transmit current continuously from said source to oneof said windings, an intercom nection between said phase windings, a second group of electric valves connected to return said current continuously from another of said wind- 'ings to said source, and means for controlling the conductivity of said groups of valves.

4. An electric valve converting system comprising an alternating current supply. circuit,

electric translating apparatus including a pair of inductive windings, an electric valve interconnecting each terminal of one of said windings with each terminal of said alternating current circuit, said. valves being similarly connected with respect to said supply circuit, an interconnection between said windings, and an electric valve interconnecting each terminal of the other of said windings with each terminal of said alternating current circuit in a sense opposite to that of said first mentioned valves, and means for controlling the com! 1ctivity of said valves.

5. An electric valve converting system comprising an alternating current supply circuit, electric translating apparatus including a pair of inductive windings each provided With an electrical neutral, a reactance device interconnecting said neutrals, an electric valve interconnecting each terminal of one of said windings and each terminal of said alternating current circuit, said valves being similarly connected with respect to said supply circuit, an electric valve interconnecting each terminal of the other of said windings with each terminal of said supply circuit in a sense opposite to that of said first mentioned .valves, and means for controlling the conductivity of said valves.

6. An electric valve converting system comprising a polyphase alternating, current supply circuit, electric translating apparatus including a plurality of inductive windings, electric valve means for supplying current to one of said windings from one phase of said supply circuit, a connection between said windings, other electric valve means for returning said current from another of said windings to another phase of said supply circuit, and means for controlling the conductivity of said electric valve means.

7. An electric valve converting system comprising a polyphase alternating current supply circuit, polyphase electric translating apparatus comprising a pair of inductive windings each provided with an electric neutral, a reactance device interconnecting said neutrals, an electric valve interconnecting each terminal of one of said windings with one phase of said supply circuit, said valves being similarly connected with respect to said supply circuit, an electric valve interconnecting each terminal of the other of said windings with another phase of said supply circuit in a sense opposite to that of said first mentioned valves, and means for controllingthe conductivity of said valves.

8. An electric valve converting system comprising an alternating current supply circuit, polyphase electric translating apparatus including a pair of polyphase inductive networks each provided with an electrical neutral, a reactance device interconnecting said neutrals, an electric valve interconnecting each phase terminal of one of said networks with each terminal of said supply circuit, said valves being similarly connected with respect to said supply circuit, an electric valvexinterconnecting each phase terminal of the other "or said networks with each terminal of said supply circuit in a sense opposite to that of electric valve means. i

10. The method of energizing a polyphase electric translating apparatus comprising a plurality of phase windings from a source of alternating current which comprises continuously supplying current from said source to one of said phase windings, transmitting said current to another of said phase windings, and continuously return.- ing said current from said last mentioned phase winding to said source.

11. The method of energizing a. polyphase electric translating apparatus comprising a plurality of phase windings from a source of alternating unidirectional current to one of said phase windings, periodically changing the point of entrance of said current from one terminal to the other, transmitting said unidirectional current to a second of said phase windings, continuously returning said current from said second phase winding to said source, and periodically changing the point of exit of said current from one terminal to the other of said second winding.

12. An electric valve frequency changing system comprising a source of alternating current, a load circuit comprising a plurality of phase windings, a group of similarly connected electric valves interconnecting one of said phase windings and said source, a second group of electric valves interconnecting another of said phase windings and said source, said second group of valves being connected oppositely to said first group with respect to said source, and means for controlling the conductivities of said valves at a variable frequency to supply variable frequency alternating current to said load circuit.

13. An electric valve converting system comprising a source of alternating current, an alternating current dynamo-electric machine provided with a plurality of phase windings, a group of similarly connected electric valves intercom? necting one of said phase windings and said source, an interconnection between said, phase windings, a second group of electric valves interconnecting another of said phase windings and said source, said second group of valves being connected oppositely to said first group with respect to said source, and means for controlling the conductivities of .'sai d'valves at a variable frequency to vary-the speed of said machine.

14. An electric valve converting system comprising a source of current, a dynamo-electric machine provided with a plurality of armature terminals, a plurality of electric valves interconnecting said source, and said terminals for commutating the current therebetween, said system including a circuit carrying unidirectional current, and a reactance device connected in said unidirectional current circuit to maintain substantially steady current therein and serving as a source of excitation for said machine.

15. An electric valve converting system com.- prising a source of alternating current, a dynamoelectric .machine provided with a plurality of armature phase windings a plurality of electric valves interconnecting said' phase windings and said source and acting to rectify said alternating current and commutate it between said phase windings, said phase windings and valves being connected to form a direct current circuit, and a reactance device in said direct current circuit to smooth out the ripples of the supply frequency, said reactance serving also as an exciting winding for said machine.

16. An electric valve converting system comprising a source of current, a motor provided with apair of armature phase windings each provided with an electrical neutral, a first group of similarly connected electric valves interconnecting one of said windings and said source, an exciting winding for said motor connected between the neutrals of said windings, a second group of electric valves interconnecting the other phase winding with said source, said second group being connected oppositely to said first group with respect to said source, and means for controlling the conductivity of said valves. I

1'7. An electric valve converting system comrality of electric valves interconnecting said source and said windings for commutating the current therebetween, said system including a circuit carrying unidirectional current, a reactance device connected in said unidirectional current circuit to maintain substantially steady current therein and serving as a source of excitation for said motor, and a variable impedance device in circuit with said reactance device to vary the speed-torque characteristics of said motor.

18. An electric valve converting system comprising a source of current, a motor provided with a pair of armature phase windings each having an electrical neutral, a first group of similarly connected electric valves-interconnecting one of said windings and said source, an exciting winding for said motor connected between the neutrals of said windings a second group of electric valves interconnecting the other phase winding with said source, said second group being connected oppositely to said first group with respect to said source, means for controlling the conductivity of said valves in accordance with an operating condition of said motor, whereby the motor is given series motor characteristics, and a variable impedance device in circuit with said exciting winding for varying the speed-torque characteristics of said motor.

19. An electric valve converting system comprising a source of current, a motor provided with a pair of armature phase windings each having -35 an electrical neutral, a first group of similarly connected electric valves interconnecting one of said windings and said source, an exciting winding for said motor connected between the neutrals of said windings, a second group of electric valves interconnecting the other phase winding with said source, said second group being connected oppositely to said first group with respect to said source, means for controlling the con ductivity of said valves in accordance with an operating condition of said motor, whereby said motor is given series motor characteristics, a reactance device in series with said exciting winding, and a variable resistor connected in parallel with said exciting winding to vary the speedtorque characteristics of said motor.

20. An electric valve converting system comprising a source 'of alternating current, an electric translating apparatus, a plurality of electric valves interconnecting said source and said apparatus, each of said valves being provided with an anode, a cathode, and a control grid; a grid circuit for each of said valves including a distributor and an alternating potential derived from said source, and means for varying the phase of said alternating potential to vary the energization of said apparatus.

21. An electric valve converting system comprising a source of alternating current, a dynamo-electric machine provided with a plurality of armature terminals, a plurality of electric valves interconnecting said source and said terminals for commutating the current therebetween, each of said valves being provided with an anode, a cathode, and a control grid, a distributor provided with a brush for each of said armature terminals, a phase shifting device energized from said source, a plurality of circuits energized from said phase shifting device and including a brush of said distributor and an impedance device, and a circuit for exciting the grids of the valves associated with each terminal of said armature winding with the potential across one of said impedance devices.

22. An electric valve converting system comprising a source of alternating current, a motor provided with a plurality of armature terminals, a plurality of electric valves interconnecting said source and said terminals for commutating the current therebetween, each of said valves being provided with an anode, a cathode, and a control grid, a direct current exciting winding for said motor, a distributor driven by said motor and provided with a brush for each .of said motor terminals, a phase shitting device energized from said source, a plurality of circuits energized from said phase shifting device and including a brush of said distributor and a resistor, and a circuit for exciting the grids of the valves associated 'with each terminal of said armature winding with the potential across one of said resistors.

23. The method of operating a dynamo-electric machine provided with a plurality of armature windings andassociated terminals from a source of alternating current through a plurality of electric valves provided with control grids which comprises applying successively to the grids of the valves associated with the, several armature terminals an alternating potential derived from said source, and varying the phase of W said alternating potential to vary the energizetion of said machine.

24. The method of operating a dynamo-electric machine provided with a plurality of armature windings and associated terminals from a source of alternating current through a plurality of electric valves provided with control grids which comprises applying an alternating potential derived from said source to the grids of the valves associated with the terminal of an armature winding in .torque producing position, successively transferring said grid excitation to.the valves associated with successive armature terminals as their respective windings move into torque producing position, and varying the phase of said alternating potential to vary the energization of said machine.

25. The method of starting a motor provided with a plurality of armature windings and associated terminals from a source of alternating current through a plurality of electric valves provided with control grids which comprises applying to the grids of the valves associated with the terminal of an armature winding in torque producing position, an alternating potential derived from said source and retarded in phase with respect thereto, successively transferring said grid excitation to the valves associated with successive armature terminals as their respective windings move into torque producing position, and advancing the phase of said alternating potential to increase the energization of said motor as it increases in speed.

26. An electric valve converting system comprising a source of current, a dynamo-electric machine provided with a plurality of armature terminals, a plurality of. electric valves interconnecting said source and said terminals for commutating the current therebetween, each of said valvesbeing provided with a control grid, a direct current exciting winding for said machine, and grid circuits for the several valves energized fromsaid armature terminals.

27. An electric valve converting system comprising a source of current, a dynamo-electric machine provided with a plurality of armature terminals, a plurality of electric valves interconnecting said source and said terminals ior commutating the current therebetween, each of said valves being provided with a control grid, a direct current exciting winding for said machine, means for exciting said grids in accordance with the counter-electromotive force of said machine, and means for determining the phase relation between said electromotive force and said grid excitation.

28. An electric valve converting system comprising a source of current, a motor provided with aplurality cf armature terminals, a plurality of electric valves interconnecting said source and said terminals for comrnutating the current'therebetween, each of said valves being provided with a control grid, 2. direct current exciting winding for said motor, a control circuit for said grids energized from said motor terminals, and a manually operable phase shifting device interposed in said control circuit.

29. An electric valve converting system comprising a source of alternating current, a motor provided with a plurality of armature terminals,

a plurality of electric valves interconnecting said source and said terminals for commutating the current therebetween, each of' said valves being provided with a control grid, a direct current exciting winding for said motor, a grid circuit for each of said valves including a source of potential derived from said armature terminals, a distributor, and a source of alternating potential derived from said source, means for varying the phase of said alternating potential to vary the energization of said motor, and means for selectively disconnecting either of the sources of potential in said grid circuit.

30; An electric valve converting system comprising a source of alternating current, a motor provided with a plurality of armature terminals, a plurality-of electric valves interconnecting said source and said terminals for commutating the current therebetween, each of said valves being provided with a control grid, a direct current exciting winding for said motor, means for exciting said grids for motor speeds below approximately -'half synchronous speed comprising a distributor driven by said motor, a source of alternating po tential derived from said source of alternating current, and means for varying the phase of said alternating potential to vary the speed of the motor, and means for exciting said grids for higher motor speeds comprising a source of grid potential derived from said armature terminals.

31. The method of starting and operating a -motor provided with a plurality of armature cessively transferring said grid excitation to the valves associated with successive armature terminals as their respective windings move into torque producing position, advancing the phase of said alternating potential to increase the energization of said motor as it increases in speed,

' and thereafter impressing upon said grids a potential determined by the counter-electromotive force of said motor.

32. An electric valve converting system com prising a source of alternating current, a dynarno-electric machine provided with a plurality of armature terminals, and a plurality oi. electric valves interconnecting said source and said terminals for commutating the current therecetween, said system including a reactance device provided with an exciting winding energized with a unidirectional magnetomotive force, said reactance device serving as a source of excitation for said machine.

33. In a control system for a motor having a plurality'of armature windings and a field winding each divided into a' plurality of angularly displaced sections, an alternating current supply line, electron discharge means connected with the windings of the motor for controlling the energization thereof from said supply line, a source of potential, adjustable means controlling the operation of said means by controlling'the connection of said source therewith, and means for producing the simultaneous energization of at least two portions of different ones of said arma ture windings. I

34. In a controlsystem for a motor-having a plurality of armature windings and a field wind-- ing, a polyphase alternating current supply line connected with said windings, electron discharge means connected with the armature windings of the motor for controlling the energization thereof. a source of potential, adjustable means controlling the operation of said means by controlling the connection of said source therewith, and means for obtaining simultaneous energization of portions of at least two of said armature windings supplied with current from said supply line. 1

35. In a control system for a motor having a plurality of armature windings and a field winding each divided into a plurality of angularly displaced sections, an alternating current supplyline, electron discharge means connected with said line and the armature windings of the motor r controlling the energization thereof, a source of direct current, means for obtaining low potent al alternating current from said line, means connected with said source and with the said low potential alternating current means for controll'ng the operation of said electric discharge means, and means for obtaining simultaneous energization of at least two portions of different ones of said armature windings.

36. In a control system for a motor having a rurality of armature windings and a field wind-' ing, a polyphase alternating current supply line, electron discharge apparatus connected with the w'ndings of the motor, and means controlling the operation of said apparatus to produce the simultaneous energization of portions of at least two of said armature windings by transmitting current from one phase of said supply line to a different phase thereof through said windings.

37. In a control system for a motor having a plurality of armature windings each divided into a plurality of angularly displace-d sections and a field winding, an alternating current supply line connected with the motor windings, electron discharge apparatus having anodes with associated ccntrol electrodes, a source of potential, distributor means for co-operatively controlling the connection of said source with the control electrodes to control the operation of said apparatus to cause the sequential energization of the respective sections of each one of said armature windings, and means for obtaining the simultaneous energization of at least two sections of diflerent ones of said armature windings. I

38. In a control system for a motor having. a

plurality of armature windings each divided into plurality of angularly displaced sections and a field winding, an alternating current supply line connected with the motor windings, electron discharge apparatus for controlling the flow of enargy from .said line through said motor,'a source of potential, distributor means for controlling the connection of the control electrodes with said source to control the operation of said device to cause the sequential energization of each one of the respective sections of said armature windings,

means for producing the simultaneous energizaiicn of at least two sections of different ones of said armature windings, and means for controlmg the connection of said source with said distributor means.

39. In a motor control system, an alternating current supply line, a inotor having rotating field windings and a plurality of armature windings each divided into a plurality of star connected portions, electron discharge apparatus connected with the motor windings and controlling the flow of current therethrough, means for controlling the operation of said apparatus to cause the sequential energization of different portions of each one of said armature windings, and means for obtaining the simultaneous energization of at least two portions of difierent ones of said armature windings.

40. In a control system for amotor having a plurality of armature windings each divided into a plurality of displaced sections and a field winding, a polyphase alternating current supply line, electron discharge apparatus interconnecting said supply line with the several sections of the armature windings of the motor for controlling the energization thereof, a source of direct current;

means for obtaining low potential current from said line, means connected'with said source and with the first said means for controlling the operation of said apparatus, and means for transmitting current from one phase of said line through certain of said armature windings to another phase of said line thereby obtaining simultaneous energization of a plurality of portions of difierent ones of said armature windings.

41. In a control system for a motor having a plurality of armature windings and a field winding each divided into a plurality of angularly displaced sections, an alternating current supply line connected with said windings, electron discharge apparatus connected with the windings of the motor for controlling the energizationthereof, a source of potential, adjustable means responsive to the speed of said motor for controlling the operation of said apparatus by controlling the connection 01' said source therewith, and means for obtaining simultaneous energize.- tion of at least two portions of different ones of said armature windings.

42. In a control system for a motor having a plurality of armature windings and a field winding each divided into a plurality of angularly displaced sections, an alternating current supply line connected with said windings, electron discharge apparatus connected with the armature windings of the motor for controlling the energization thereof, a source of direct current, means for obtaining low potential alternating current from said line, means connected with said source and with the first said means for controlling the operation of said apparatus in response to the speed or said motor, and means for obtaining simultaneous energization of at least two portions 01' different ones of said armature windings.

43. In a control system for a motor having a plurality of armature windings each divided into a plurality! of displaced sections and a field winding, 9. polyphase alternating current supply line connected with said windings, an electron discharge apparatus connected with the several sections of the armature windings of the motor for controlling the energization thereof, a source of direct current, means for obtaining low' potential current from said line, means connected with said source and with the first said means for controlling the operation of said apparatus in accordance with the speed of said motor, and means for obtaining simultaneous energization of a plurality of portions of different ones of said I armature windings.

44. An electric valve converting system comprising a source of alternating current, polyphase electric translating apparatus including a dynamo-electric machine provided with a plurality of phase windings, electric valve means interconnecting said phase. winding with said source,

' means for simultaneously energizing at least portions of two of said phase windings, and means for controlling the conductivity of said electric valve means.

45. An. electric valve converting system comprising a source of alternating current, a dynamo-electric machine provided with a plurality i of armature windings) electric valve means interconnecting said source and said armature windings for commutating the current therebetween, said system including a circuit carryingunidirectional current, and a reactance device connected in said unidirectional current circuit and serving as a source of excitation for said machine.

46. An electric valve converting system comprising a source of alternating current, an electric translating apparatus, electric valve means interconnecting said source and said apparatus, said valve means being provided with a plurality of anodes, a control grid for each of said anodes, a grid circuit for each of said grids including distributor means and an alternating potential derived from said source, and means for varying the phase of said alternating potential with respect to said source to vary the energization of said apparatus.

comprises applying successively to the grids of the valvepaths associated with the several electric terminals an alternating potential derived from said source, and varying the phase of said alternating potential to vary'the energization of said machine.

ERNST F. w. ALExANDERsoN. 

